The invention relates generally to catheters, and more particularly, to steerable catheters for performing electrophysiological procedures, such as mapping electrical signals emitted from conductive cardiac tissue and ablating aberrant cardiac tissue at the point of arrhythmia origination in order to terminate the arrhythmia.
The heart beat in a healthy human is controlled by the sinoatrial node (S-A node) located in the wall of the right atrium. The S-A node generates action potentials which are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (A-V node) which in turn transmits the signals throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth of or damage to the conductive tissue in the heart can interfere with the passage of electrical signals from the S-A and A-V nodes resulting in disturbances to the normal rhythm of the heart, referred to as cardiac arrhythmia.
If the arrhythmia is refractory to medication, an alternative treatment is to ablate the aberrant conductive tissue. However, that aberrant tissue must first be located. One technique involves the electrical mapping of signals emanating from conductive cardiac tissue to locate the aberrant tissue causing the arrhythmia. Ablation may then be performed. Ablation of the aberrant conductive tissue usually controls the arrhythmia and allows the heart rhythm to return to an acceptable level.
One conventional method for mapping the electrical signals from conductive heart tissue is to provide an array of electrodes on the distal extremity of a catheter and place those electrodes in contact with the interior of a patient's heart. Typically, the catheter is introduced into the cardiovascular system of the patient through a blood vessel and advanced to an endocardial site such as the atrium or ventricle of the heart. When placed into the blood vessel, the catheter must follow the irregularly shaped path defined by the blood vessel and branch vessels until the distal end of the catheter reaches the desired location. To assist in steering the catheter, some catheters have a curved distal tip. While this pre-formed curve may fit the curves of some blood vessels, it rarely fits all anatomical possibilities. Greater freedom of movement is desirable.
To achieve greater control over the movement of the catheter in steering it through the cardiovascular system to the desired location in the patient, prior catheters have used guide wires to selectively vary the shape of the distal tip of the catheter. In another technique, a control line is attached at a point adjacent the distal tip of the catheter. Pulling the proximal end of the control line causes the distal tip of the catheter to bend in one direction. Other designs have used multiple control lines to obtain bending in multiple directions; however, the size of the catheter increases. Larger catheters are undesirable due to the difficulties involved in moving them through the patient's cardiovascular system and the increased blockage to blood flow. While the control line approach provides increased freedom of control over the movement of the distal end of the catheter, its effect in prior techniques is limited to an arc with a fixed radius.
In another technique, a mandrel or guide wire is also located in the catheter in addition to the control line and is moved to alter the radius of bend of the distal end of the catheter. The mandrel would be moved more towards the distal end or more towards the proximal end of the catheter to alter the radius of bend of the distal end. While such an approach has been found to yield improved control over the movement of the distal end, the disclosed technique required that the physician use two hands to exert this control. Additionally, no means were provided for holding the mandrel and control line in position once the desired bend was obtained thereby resulting in the physician having to hold both the mandrel end and the operating mechanism of the control line. Requiring the use of two hands for the steering function alone restricts the physician from performing other tasks at the same time.
Another consideration in keeping the catheter small in size but providing an increased steering capability is the torsional rigidity of the catheter. In catheters with low torsional rigidity, torsion may accumulate as the proximal end of the catheter is twisted by the physician. Then as the distal end finally begins rotating, the accumulated torsional moment will tend to unwind the catheter, resulting in rapid rotation of the tip inside the blood vessel. Such unwinding may result in the distal tip of the catheter overshooting the branch vessel entrance then requiring further steering manipulation on the part of the physician lengthening the procedure. Thus it is desirable to have increased torsional rigidity of the catheter so that rotating the proximal end of the catheter will result in immediate rotation at the distal end; i.e., immediate torque reaction.
A further consideration in navigating the catheter into the desired position in the patient is the bending rigidity or stiffness of the catheter. In some cases, increased force is required to advance the distal end of the catheter through a certain vessel position or to hold it against a particular site such as buttressing the catheter against a wall of the aorta or against a valve lip. However, decreased bending rigidity is beneficial in some cases. Therefore it would be desirable to provide variable bending rigidity of the catheter to provide increased steering and positioning control. Such a feature would be desirable in an electrophysiological procedure catheter due to the requirement for navigation completely into the heart and for continued contact with particular tissue during the beating action of the heart. Additionally, it would be desirable to incorporate the control means over the bending rigidity of the catheter into the same control device as is used for the other steering mechanisms.
Frequently, the position of the distal portion of the catheter within the heart may have to be adjusted one or more times in order to provide a complete and comprehensive view of the signals from the electrically conductive heart tissue which is necessary to detect the point where the arrhythmia originates. Once the origination point for the arrhythmia is determined, the conductive heart tissue at the site can be ablated. RF heating is one technique typically used for ablation. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels. Increased and easier control over the steering and positioning of the catheter would facilitate the mapping and ablation of the heart tissue.
Hence, those skilled in the art have recognized the need for a catheter for use in electrophysiological procedures which provides increased control over steering and positioning the catheter while not increasing the size of the catheter. It has also been recognized as desirable a catheter with increased torsional rigidity and a means for providing increased control over the axial rigidity of the catheter. The present invention fulfills these needs and others.